Lead anode for chromium plating



June 2 1958 w. CIB ULSKIS ETAL 2,840,523

LEAD ANODE FOR CHROMIUM PLATING Filed Feb. 2. 1955 1 Mb I I:

INVENTORS WALTER S. CIBULSKIS HENRY MAHLSTEDT MEYER SHACAT W4,%IM

ATTORNEYS United States Patent LEAD ANODE FOR CHROMIUM PLATING Application February 2, 1955, Serial No. 485,656

1 Claim. (Cl. 204-286) This invention relates to an insoluble lead anode for chromic acid chromium plating baths having substantial advantages over conventional lead anodes used for this purpose, particularly in respect of its capacity to carry a higher surface current density than conventional anodes of equal cross-sectional area, and its freedom from buildup of chromate deposits. Other advantages will appear hereinafter.

The invention may be better understood by referring to the accompanying drawing wherein Fig. 1 is a partially sectioned, broken side view of the anode and Fig. 2 is a sectional view along the line 22 of Fig. 1.

As shown, the anode comprises an upper hook portion 1, a lower anode portion 2, and an intermediate portion 3 joining the upper and lower portions. The upper portion comprises a hook 4 for supporting the anode on a tank bar, a lower end piece 5, and a bar 6 connecting the hook to the end piece. The end piece is somewhat enlarged and has a conical shape; it is adapted to be engaged by the portion 3, for which purpose it is preferably provided with a plurality of circular projections 7, 8, 9, and 10 extending laterally therefrom and spaced one above the other. The portion 3 comprises an enlarged cylindrically shaped part or sheath 11 having the end piece embedded centrally therein. To improve the adherence between the part 11 and piece 5, a layer 12 of tin or solder may first be applied to piece 5 as by hot dipping. Part 11 has an upwardly extending sleeve 13 enclosing a portion of the connecting bar 6 and also has a short extension 14 extending below the end piece. The lower portion 2 comprises a cylindrically shaped, rigid anode member or length 15 joined to part 11 by means of a fused lead joint 16 between the member and the extension 14. Member 15 has a solid cross section of circular shape, as shown in Fig. 2.

The upper portion 1 is made of copper or a high copper alloy, such as copper-tin alloy, and is preferably formed by casting. Hook 4 has the usual knife edge 4a on its under or contact side, the usual wedge-shaped cross section (not shown), and the usual handle 4b; the hook may be long or short as required and may have other suitable shapes than as shown. The intermediate portion 3 is ice 94% lead-2% tin-4% antimony alloy, and is lead burned to part 11. It will be understood that member 15 may be as long as desired, depending on the depth of the plating tank; its diameter is also variable, usually lying between 0.5 and 3 inches. Member 15 is conveniently formed by extrusion. Its preferred cross-sectional shape is circular, although it can be somewhat out of round provided it is substantially circular. Preferably, too, its outer surface is smooth, as shown in Fig. 2, but surfaces that are serrated, ribbed, grooved, knurled, etc. are also suitable.

As indicated, the anode provides a maximum conductivity per surface area, the cylindrical sides of length 15 affording a greater active working surface than heretofore available. Current is distributed through the complete circumference of length 15, as shown by the uniform gassing that takes place, thus eliminating chromate buildup on the surfaces and favoring a more even current distribution. The absence of chromate deposition represents a substantial improvement over conventional lead anodes, particularly the flat anode where chromate tends, to build up on the surface facing the plating tank lining, that is, the surface turned away from the work. Due to its circular shape, the length 15 can handle high surface current densities without overheating; this characteristic, plus its unusual rigidity, eliminate danger of warping. Its circular peroxide coatings, which provide increased protection made of lead or a high lead alloy and is cast about the portion 1 so that sheath 11 and sleeve 13, respectively, enclose piece 5 and connecting bar 6. The extension 14 of the sheath 11 is preferably formed so as to terminate at a point generally indicated at 14a; in other words, the lower part of extension 14 has the form of an inverted cone of short height, thus providing a space 14b for receiving fused lead to form the joint 16. Member 15, like portion 3, is made of lead or a high lead alloy, such as a against corrosion. Cleaning is easier, and the service life is longer.

In the light of the foregoing description, the following I is claimed:

An insoluble lead anode for a chromic acid chromium plating bath, comprising an upper portion of copper, an elongated lower portion of lead, and an intermediate portion of lead joining the upper vand lower portions, the upper portion being integral and having a hook at its upper end and an enlarged conical portion at its lower end and a shank intermediate the hook and enlarged conical portion, the intermediate portion being cylindrical and the enlarged conical portion being coaxial with and disposed entirely within the intermediate portion, the lower portion having a thickness in any lateral direction less than the diameter of the intermediate portion, the shank of the upper portion being inclined from the common axis of the enlarged conical portion and the intermediate portion and joining the enlarged conical portion at an obtuse angle, and a sleeve integral with the intermediate portion and of less diameter than the intermediate portion, the sleeve being inclined with the shank from the axis of the intermediate portion and enclosing a portion of the shank.

References Cited in the file of this patent UNITED STATES PATENTS 733,602 Starrett July 14, 1903 903,939 Winsom Nov. 17, 1908 2,109,975 Ott Mar. 1, 1938 2,125,037 Sykes July 26, 1938 2,274,056 Geiger Feb. 24, 1942 2,507,694 Cox May 16, 1950 2,723,230 Godsey Nov. 8, 1955 FOREIGN PATENTS 284 Great Britain Jan. 5, 1914 

